膨胀土地基中大比例模型桩浸水试验研究

通过对埋设在膨胀土地基中的一试桩的长时间浸水试验观测，模拟了自然降雨气候条件下单桩位移、沿桩身轴力、侧摩阻力分布、地基胀缩及其时间变化等基桩一系列工作性状和桩-土共同作用规律。试验结果显示：桩顶位移呈现出先下沉后回升并最后趋于稳定的3阶段特征；桩身全长受拉，轴力沿桩身分布呈“波峰”形态。基桩的最大轴力位于桩的中下部，轴力峰值历经由小到大的过程；中性点在浸水过程中，其位置有从桩下部上移的现象；桩侧摩阻力与桩端阻力荷载分担比随时间呈现出先减小后增大并渐趋稳定的3阶段特征。研究结果对膨胀土地基中的桩基设计和施工提供了理论依据。     

基于BP神经网络的矿车运行时矿井摩擦阻力的预测*

为了快速有效地确定矿车等运输设备在巷道内运行时矿井摩擦阻力的变化情况,克服模拟软件计算量和现场实测工作量大的问题,以巷道风流速度、矿车运行速度、阻塞比、矿车长度4个矿车运行时巷道摩擦阻力的影响因素作为切入点,采用动网格技术模拟得到矿车在巷道内运行时有关矿井摩擦阻力的数据,以此为样本构建基于BP神经网络的矿井摩擦阻力预测模型,运用MATLAB软件进行网络训练,并将BP神经网络预测值与FLUENT模拟值进行对比。研究结果表明:BP神经网络结构比较简单,能以较快速度收敛,预测值与模拟值最大误差在7%以内,该神经网络模型用于求解矿车等运输设备在巷道内运行时摩擦阻力的变化情况是可行的。     

沥青涂层对桩侧摩阻力影响的试验研究

采用改进直剪仪模拟桩与土之间的滑动摩擦,研究了沥青涂层对桩侧摩阻力的影响。试验结果表明,桩侧摩阻力与土的类型、法向应力有关,随着法向应力的增长,滑动摩阻力也相应增长,且增长近似呈线性关系;在一定的法向应力下,沥青涂层对减小滑动摩阻力有一定的作用,随着法向应力的增长,沥青涂层亦会导致滑动摩阻力增加。     

On the parameterization of the roughness length for the air-sea interface in free convection

The roughness length at the air-sea interface during free convection (z_0fc) is mainly related to the convective velocity (w_*) rather than the friction velocity (u_*). The parameterization of z_0fc with w _* ² /g as proposed by Abdella and DAlessio in 2003 is evaluated. It is shown that their proposed formula is consistent with field measurements. In order to avoid self-correlation by using u_*, a new parameterization of w_* with wind speed (U_z) at height z and stability parameter (z/L, where L is the buoyancy length) is proposed. This new formula for w_* is in agreement with an independent field result.     

The Surface Roughness of a Rubber Soling Material Determines the Coefficient of Friction on Water-Lubricated Surfaces

For more than a decade, evidence has been accumulating that points to the fact that the microscopic roughness of the footwear soling surface is a major determinant of slip-resistance on lubricated surfaces, but conclusive experimental proof has been lacking. This article describes an experiment in which five pairs of shoes were soled with the same rubber compound. Four of the pairs were abraded by different grades of grit to produce a range of roughness values. The coefficient of friction (CoF) of the five solings was then measured repeatedly by the walking traction method on wet surfaces including glazed wall tiles, vinyl asbestos coated with the wax floor polish, and both sides of a sheet of float glass. The Kruskal-Wallis statistical test proved beyond doubt that the soling roughness is a major factor in determining the CoF of this rubber soling material; p < 10⁻⁵. Nearly all of the grip was due to surface roughness of the soling material on these atypically smooth floors, although the surface roughness of the floors also had a significant effect on CoF; p < 0.003. Float glass is shown to be a promising reference floor material for the measurement of CoF of footwear; there was no statistical difference between results for the two sides of the glass sheet. Float glass could be used in the development of a standard CoF test method because new sheets of glass from the same manufacturer are identical and extremely smooth. The specification of CoF values for solings/floors combinations in lubricated conditions is of little value unless associated with roughness measurements and knowledge of how wear will affect the surface roughness of the sole. This article reports the first evidence that any specification of flooring by measuring CoF based on dry surfaces could lead to an increase in the number of injuries caused by slipping on the wet surfaces. Published by Elsevier Science Ltd     

石棉摩擦材料废弃物制吸附剂对染料的吸附研究

以石棉摩擦材料加工废弃物为材料制得的吸附剂,在色度５０００倍溶液中对阳离子黄Ｘ－５ＧＬ的静态吸附量为１５９．６８ｍｇ／ｇ,在色度５００倍的溶液中对阳离子艳蓝ＲＬ的静态吸附量为７９．６８ｍｇ／ｇ;对毛纺厂腈纶染缸废水的处理量可达２８０ｍｌ／ｇ,对活性染料亦有较好的吸附效果,吸附饱和吸附剂可通过后处理实现资源化。     

摩擦摆隔震支座理论分析与数值模拟研究

介绍了摩擦摆隔震支座的基本构成和隔震原理.利用力学平衡原理,对摩擦摆隔震支座进行了理论分析,推导了摩擦摆隔震支座的刚度和等效粘滞阻尼比,构造了摩擦摆隔震支座的滞回模型,并探讨了该支座的自回复能力,得到了其最大残余位移计算公式.采用有限元软件ABAQUS,对摩擦摆隔震支座进行实体单元建模,模拟低周反复荷载作用下,该支座的...     

考虑峰后软化的圆形巷道稳定性分析及工程应用

为获得更准确的巷道围岩应力分布和变形特征,基于统一强度理论,考虑围岩塑性软化和中间主应力的影响,引入塑性软化参数,推导出巷道围岩弹塑性区应力、塑性区范围和位移的表达式。通过算例分析,得到塑性软化系数和中间主应力等相关参数对巷道围岩应力分布、塑性区半径和位移的影响规律。研究结果表明:随内摩擦角软化系数和黏聚力软化系数的增大,围岩塑性区半径和位移呈现先急剧后缓慢的减小趋势;中间主应力系数对巷道围岩弹塑性应力有着显著影响,中间主应力系数越大,围岩塑性区半径和位移越小。     

小井眼双阶梯水平井摩阻分析及降摩阻技术

阶梯水平井作为一种特殊水平井,是开采低渗透、薄油藏的有效途径,然而,针对小井眼双阶梯水平井,由于钻具重量有限,定向滑动钻进过程中,钻压的施加极为困难,直接关系到钻井安全。分析了小井眼双阶梯水平井摩阻产生的原因,形成了以改善接触正压力和摩擦系数为主的小井眼双阶梯水平井降摩阻配套技术,并进行了现场应用。结果表明,通过简化井身结构,增加下部钻具的柔性,改善钻具与井眼之间的间隙,优化井眼轨道类型、靶前位移及造斜率,采用强抑制低摩阻低伤害暂堵钻井液体系等配套技术措施,可降低钻井过程中的摩阻,在确保安全钻井情况下,能有效地提高机械钻速,成功实现地质钻探目的,平均砂岩钻遇率为70.4%,为小井眼双阶梯水平井提供借鉴作用。     

汽车制动系统的匹配设计

通过对汽车制动系统的原理及结构性能的探讨,进一步掌握整车新产品开发设计中制动系统的匹配计算.